1. Field of the Invention
The invention relates to a process for producing an insulation element, to an insulation element for a housing of an aero engine and also to an aero engine having a housing, in which at least one such insulation element is arranged radially above a guide vane.
2. Discussion of Background Information
In turbines of turbomachines, for example aero engines or stationary gas turbines, very high temperatures at which the strength properties of the materials commonly used are greatly reduced prevail during operation in the turbine region, in particular in the annular space. This relates primarily to the housing of low-pressure turbines. In order to limit the temperatures in the region of the housing, which also has to undertake load-bearing tasks, to an acceptable range during operation of the associated turbomachine, various measures are known. By way of example, attempts are made to internally cool the housing by supplying secondary cooling air. The disadvantage of this solution consists in the high consumption of secondary air, which has to be withdrawn from the cycle and thus reduces the overall efficiency of the engine.
A further possibility consists in the external application of cooling air, for example with what is termed “Active Clearance Control” (ACC, “Cold Air Shower”), which controls the expansion behavior of the housing and therefore the radial clearances and reduces the material temperature of the housing. Disadvantages which are to be mentioned here are likewise the consumption of secondary air, but also the relatively minor ability to influence the effective material temperature and also the additional weight for the ACC and the required pipes.
It is commonly the case that insulation elements are arranged between guide vanes and the housing in order to ensure that the material temperature at the housing is reduced. These insulation elements generally consist of a thin sheet-metal jacket filled with swelling insulation material (for example a mineral substance). By way of example, EP 0 643 208 A1 discloses a thermal insulation arrangement, in which use is made of an insulation element made of a deformable metal foil which is filled with a thermal insulation material of a composite material mixture that increases its volume by up to 300% of its starting thickness when heated, such that the insulation element bears completely against the inner walls of an associated hollow space of the housing.
Through the configuration with a thin sheet-metal jacket, however, narrow limits are set for the shaping of the insulation element, as a result of which in some cases an optimum insulation action cannot be provided. In addition, as a result of the considerable changes in volume, the insulation element has a relatively low lifespan.